1. Field of the Invention
The invention relates to a gantry stacker for transporting and stacking freight containers. The invention may be used whenever several containers are deposited in a close side-by-side relationship by a crane in transhipment ports and whenever it is necessary to transport, stack or position the side-by-side freight containers for conventional gantry stackers to ensure further shipment.
2. The Prior Art
On transhipment docks, in particular in port facilities, containers are usually picked up, transported and when necessary stacked on the ship or in the port facility by means of gantry crane spreaders for loading and unloading ships. Such a gantry crane has been described in German Patent No. DE 197 26 359 A1 for example.
Containers that have been deposited in the port facility are next picked up by gantry lift trucks and transhipped to the port facility where they are loaded onto other vehicles such as road vehicles or stacked appropriately.
German Patent No. DE 32 221 49 A1 describes a gantry stacker for picking up containers and for transporting them. These vehicles are suited for picking up superposed containers and have therefor a corresponding height. On either side of two chassis beams there are at least two, but often even several steerable wheels. These chassis beams have to be of a narrow implementation for the gantry stacker to be capable of traveling between the containers in narrow alleys. For this reason, these chassis beams are often configured so that engines, gears and other parts needed for displacement are disposed therein. Usually, two supports are located on the chassis beams. On the supports are located the hoist, the overhead frame, the driver's cab and engines usually constituting combustion engines, e.g., diesel engines, supplying the current for the drive in the wheels.
A spreader for taking hold of containers and for transporting them on a gantry lift truck has been described in German Patent No. DE 103 55 946.9. This spreader is not only slidable laterally but also movable alongside the container so that the gantry lift truck needs not correct mispositions by traveling moves.
Spreaders disposed one behind the other and by means of which two 20 foot containers are transportable are described in International Application WO 01/62657 A1. The spreader apparatus proposed is also suited for taking hold of and for stacking very long containers.
In order to increase the transport capacity in port facilities, gantry stackers have been developed with a spreader that can pick up and transport two containers standing behind each other. Such gantry cranes have been described in European Patent No. EP 0 960 067 B1 for example.
In order to increase the transport capacity in the port facility, gantry stackers have been developed with a longer spreader for several containers to be transported, standing one behind the other. Such stackers are known from literature. Recent developments for dealing with even higher container handling rates provide for the gantry or ship-to-shore cranes to be equipped with what are termed tandem spreader systems. These tandem spreader systems are used to take hold of several, preferably two, side-by-side 40 feet freight containers or four 20 feet containers standing side-by-side and behind each other, and to transport them from the port facility to the ship or from the ship to the port facility.
For shore-to-ship transport, this implies that several containers are placed so as to stand side-by-side for the tandem spreader system of the ship-to-shore crane to take hold of them. After simultaneous ship-to-shore transport of several containers, further transportation of the containers deposited on the shore can occur in a fast and reliable way, since too slow transport in the port will limit the unloading speed of the gantry crane. In their actual mode of construction, the known gantry stackers for transporting and stacking freight containers however are not capable of transporting two containers standing side-by-side, since there is no alley between them for the traveling beam to pass. Further, their hoists are not suited for separating two containers standing side by side.
International Application No. WO 2005/090223 A1 describes a spreader system for taking hold of containers and for transporting them by means of which two containers disposed in a side-by-side relationship are taken hold of and transported. In the normal state, both spreaders are solidly joined together. There is however also the possibility to separate the two spreaders with a hydraulic device and to deposit containers at a certain distance from each other. Another possibility is to take hold of two containers and to deposit them independent of each other. However, this requires two trolleys that can travel independently of each other. Further, a hydraulic mechanism is disposed in the upper region of the spreader so that the spreader has a great overall height. For gantry cranes, this overall height is not problematic but is a problem when utilized on a gantry stacker, because it increases the height of the gantry stacker, which should not exceed certain overall heights.
International Application Nos. WO 2006/083230 A1 and WO 03/104132 A1 describe other solutions in which side-by-side spreaders are capable of being moved apart or toward each other by means of lifting mechanisms in order to transport containers. As a result, containers standing together can be taken hold of, separated from each other and then deposited again. Irrespective of the fact that such lifting mechanisms consist of a plurality of parts and are of high weight and prone to failure as a result thereof, they suffer from the drawback of being disposed above the spreader so that they are not suited for being mounted in gantry stackers which have limited weight and overall height.
It is not possible to travel over two superimposed containers, because conventional gantry stackers are designed to have the width of one container. With the appearance of tandem spreader systems on ship-to-shore cranes and with their use for handling freight containers, the need arose to provide for a space-saving possibility of transporting and depositing freight containers so that they may be disposed in a close side-by-side relationship when picked up and reliably transported by spreader systems, and so that they may be separated from each other for conventional gantry stackers to be capable of moving and transporting them.